I am on my third one of these---the price is right, it syncs and connects just fine. BUT, the connections on the unit, and on the strap, are cheap. They corrode quickly, no matter how hard you work to dry them off after use. The result is corrupted (low) readings. I just did a 10k run and it gave me a whopping average of 87bpm (was probably 140). This is the second unit this has happened with---after the third one I'm moving on, despite the price.

As other reviews note, the maker's app is a joke (and doesn't recognize the device!). But likely you're thinking, as I did, that the last thing you need is another fitness app, and that you'll just use runmeter, strava, whatever to read the device. But few apps will work with this specific monitor, so even if it's working perfectly, you may have no way of knowing.

I found that a frustration but not a deal killer, as the primary use for which I'd purchased this (running zwift on apple tv) was, in fact, compatible.

But the monitor stopped working after two weeks (less than 10 hours total exercise time) of use. Maybe it was shipped with an old battery. Maybe it was shipped with a fine battery, but is vastly less energy efficient than other devices. Maybe it wouldn't have worked even with a new battery. I had spares a few rooms away, and could have checked. But the fact that the app (even when you get past the Chinese etc) can't even read the sensor had me so underwhelmed I couldn't be bothered to sort things out. Just ordered the Polar H10 to replace. Hate spending 3x for what is, in concept, the same thing. But I now appreciate that's as meaningful a comparison as the price of a new Tesla (or BMW) relative to a 25 year-old Chrysler with a shot transmission.

Couldn't be happier, I've been wanting to add a heart rate monitor that worked with my iPhone and Strava and this worked perfectly. It connected to my Bluetooth easily, I then went into my Strava settings (external sensors) and enabled HR and it came up instantly. I then headed out on a short ride to test it out and it worked flawlessly. I had some concern with the low price and a few of the poor reviews but so far couldn't be happier.
I will update this review should it stop working or give me headaches in the future.

I'm using this with an older Nexus 5, and getting it set up was not very straightforward.

First off, they tell you to download the app, but when searching the Google Play store you'll see nothing at all for "CooSpo". However, on the Chinese side of the instructions there are two QR codes - one takes you to a questionable-looking website for downloading the app but it is just a static background image without clickable links, and it looked sketchy anyway so I GTFO; and the other QR code took me to a 404. So the app was a no-go.

Then I just tried to pair it manually via BT. After assuming I "turned it on" by putting on the strap and attaching the sensor, I did see the device appear in the BT device list, but attempting to pair gave an error. Moving on...

I planned on using it with Endomondo, so I opened up the app and went to the bluetooth smart sensors area of the settings and it was listed there. I was able to connect from the app and it worked. ¯\_(ツ)_/¯

So you really don't need to bother with their app if you just plan on using it with a fitness app that supports it. I've only had it for a week but have used it on a run and an hour-long Insanity workout - and it maintained the connection and tracked HR throughout.

Works great with my Peloton bike. No setup required and it comes fully charged with a standard CR2032 battery. Very comfortable but suggest hand washing the strap rather putting it in the washing machine.